Rates of women who are opting for preventive mastectomies, such as Angeline Jolie, have increased by an estimated 50 percent in recent years, experts say. But many doctors are puzzled because the operation doesn't carry a 100 percent guarantee, it's major surgery -- and women have other options, from a once-a-day pill to careful monitoring.

Dr. Brad Warner, surgeon-in-chief of St. Louis Children’s Hospital, said Tuesday that he and others plan research to better understand the condition, known as CDH, or Congenital Diaphragmatic Hernia. One in 2,000 babies is diagnosed with the disease, doctors say. Half of those don’t live to their first birthday.

The condition occurs when the diaphragm, which separates the chest cavity from the abdomen, does not completely form in the womb. The contents of the belly migrate to the chest, which keeps the lungs from developing properly.

Eight babies at the St. Louis hospital died last year from the condition.

Doctors at St. Louis Children’s Hospital say they’re part of a national database registry to collect and track information on children with the condition. They plan to recruit faculty candidates that are able to explore fetal surgery intervention and are working to collect DNA for analysis.

Treatment for the birth defect varies.

Many are stillborn. Babies who die from the birth defect usually have insufficient lung tissue to survive, or develop hypertension in the blood vessels of the lungs. Medications to lower blood pressure in the lungs lower the baby’s overall blood pressure, which can be problematic.

Of those who live, some are in distress from the moment the umbilical cord is clamped; others are OK for their initial hours of life, then get worse. A third group, which is the most uncommon, initially looks good, but later exhibits signs, such as bowel sounds in the chest, that reveal the condition.

In some cases, doctors have performed surgery on pregnant women and their fetuses to try to address problems before a baby is born, but those procedures have risks. Children with CDH can grow up to be healthy adults.

Doctors say they hope to better understand predictors of good and bad outcomes for babies with the condition, as well as how to address the many complications that can arise.